1. Technical Field
The present invention relates to an electrophoretic display device used for electronic paper or the like.
2. Related Art
An electrophoretic display device includes an electrophoretic material containing a liquid dispersion medium and electrophoretic particles between a pair of electrodes and performs display by using electrophoresis of these electrophoretic particles in the dispersion medium. The electrophoretic display device controls the amplitude, polarity, waveform, application time, frequency, and the like of a voltage applied between the electrodes and displays desired information. Although the electrophoretic display device generally performs black/white binary display, it can display the image information more finely if a gray-scale display capable of changing the display brightness is performed. Therefore, realization of such a display is strongly desired. Conventionally, when performing the gray-scale display, an intermediate gray-scale is displayed by changing the voltage to be applied to the electrophoretic display device or the application time, which changes the spatial distribution state of the electrophoretic particles in the dispersion medium (see JP-A-64-86116).
However, due to the characteristic of the electrophoretic display device that maintains the display image even after the power is turned off, there has been a problem in that an after-image stands out when the gray-scale display is performed by adjusting the applied voltage and the application time, as has been done conventionally. For example, when trying to display an intermediate gray-scale such as gray from intense black or intense white, the black or the white from the previous image remains, and, even when the same gray-scale signal is input in order to display gray, a different gray ends up being displayed. Also, it has been extremely difficult to display a multiple number of gray-scales since the charged electrophoretic particles are stopped midway between the electrodes.